Microbial nutrition and growth
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LECTURES IN MICROBIOLOGY. Microbial Nutrition and Growth. Sofronio Agustin Professor. LESSON 5. Lesson 5 Topics. Microbial Nutrition Environmental Factors Microbial Growth. Microbial Nutrition. Based on intake: (a) Macronutrients (CHONPS) (b) Micronutrients (trace elements)

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Microbial nutrition and growth

LECTURES IN

MICROBIOLOGY

Microbial Nutrition and Growth

Sofronio Agustin

Professor

LESSON 5


Lesson 5 topics

Lesson 5 Topics

  • Microbial Nutrition

  • Environmental Factors

  • Microbial Growth


Microbial nutrition

Microbial Nutrition

  • Based on intake:

    (a)Macronutrients (CHONPS) (b)Micronutrients (trace elements)

  • Based on carbon content:

    (a)Organicnutrients- contain carbon

    (b)Inorganicnutrients- simple atom or molecule without carbon


Chemical composition

Chemical Composition

Bacteria are composed of different elements and molecules, with water (70%) and proteins (15%) being the most abundant.


Essential nutrients

Essential Nutrients

  • Carbon source

  • Energy Source

  • Growth Factors


Carbon source

Carbon Source

  • Autotrophs - obtain carbon from inorganic molecules like CO2

  • Heterotrophs - obtain carbon from organic matter from other life forms

    (e.g. sugar, proteins and lipids)


Energy source

Energy Source

  • Photoautotrophs and photoheterotrophs obtain energy from sunlight

  • Chemoautotrophs derive electron energy from reduced inorganic compounds

  • Chemoheterotrophs obtain electron energy from hydrogen atoms of organic compounds


Nutritional categories

Nutritional Categories

Summary of different nutritional categories of microbes based energy and carbon sources


Methanogens

Methanogens

  • Methanogens are chemoautotrophic microbes

  • Example: methane producing Archaea


Extracellular digestion

Extracellular Digestion


Cell membrane

Cell Membrane

  • Phospholipid bilayer with integral and peripheral proteins

  • “Fluid mosaic” model - phospholipids and proteins move laterally

  • Exhibits “selective permeability”


Membrane transport

Membrane Transport

  • Passive:

  • Simple diffusion

  • Facilitated diffusion

  • Osmosis

  • Active:

  • Permease

  • Group translocation

  • Endocytosis


Simple diffusion

Simple Diffusion

  • Net movement of solute from area of high concentration to a low concentrated area

  • No energy is expended

  • Down the concentration gradient (like a river flowing downstream)


Diffusion

Diffusion

A cube of sugar will diffuse from a concentrated area into a more dilute region, until an equilibrium is reached.


Facilitated diffusion

Facilitated Diffusion

  • Transport of polar molecules and ions across the membrane down their concentration gradients

  • No energy is expended (passive)

  • Carrier protein facilitates the binding and transport

    -Specificity

    -Saturation

    -Competition


Facilitated diffusion1

Facilitated Diffusion

Facilitated Diffusion: The Process


Osmosis

Osmosis

  • Diffusion of solvent (usually, water) through a permeable but selective membrane

  • Water tends to move toward higher solute concentrated areas


Tonicity

Tonicity

Fate of cells in different osmotic conditions - isotonic, hypotonic, and hypertonic solutions


Active transport

Active Transport

  • Transport of molecules against its concentration gradient

  • Requires energy and transport protein

    (Ex. Permeases and protein pumps transport sugars, amino acids, organic acids, phosphates and metal ions)

  • Group translocation transports and modifies specific sugars


Endocytosis

Endocytosis

  • Large substances are taken in by the cell but are not transported through the membrane.

  • Requires energy (active)

  • Common in eukaryotes

    - Phagocytosis

    - Pinocytosis


Active transport1

Active Transport

Example of permease, group translocation and endocytosis


Cellular transport summary

Cellular Transport : Summary


Environmental factors

Environmental Factors

  • Temperature

  • Gas

  • pH

  • Osmotic pressure

  • Other factors

  • Microbial association


Temperature

Temperature

  • Psychrophiles – (cold loving) 0 to 15 °C

  • Psychrotrophs - (food spoilage) grow between 20 to 30 °C

  • Mesophiles- (most human pathogens)

    20 to 40 °C

  • Thermophiles- (heat loving) 45 to 80 °C

  • Themoduric - (contaminants of heated food) survive in short exposures to high temp

  • Hyperthermophiles - (Archaea)


Temperature tolerance

Temperature Tolerance


Gas requirements

Gas Requirements

  • Two gases that influence microbial growth:

    (1)Oxygen

    • Respiration - terminal electron acceptor

    • Oxidizing agent - toxic forms

      (2)Carbon dioxide


Oxygen metabolites

Oxygen Metabolites

  • Superoxide radical - O2 -

  • Singlet oxygen - O2 with single electron in its valence shell

  • H2O2

    All are toxic byproducts of metabolism neutralized by enzymes SOD (superoxide dismutase), peroxidase and catalase.


Bacterial types

Bacterial Types

  • Obligate aerobe

  • Facultative anaerobe

  • Obligate anaerobe


Obligate aerobes

Obligate Aerobes

  • Require oxygen for metabolism

  • Possesses enzymes that can neutralize the toxic oxygen metabolites:

    SOD, peroxidase and catalase

  • Ex: Most fungi, protozoa, and bacteria like Bacillus sp. and Pseudomonas sp.


Obligate anaerobes

Obligate Anaerobes

  • Cannot use oxygen for metabolism

  • Do not possess SOD and catalase

  • The presence of oxygen is toxic to the cell

  • Ex: Clostridium sp. and Bacteroides sp.


Anaerobiosis

Anaerobiosis

Anaerobic culture techniques: (a) anaerobic chamber, (b) anaerobic jar


Facultative anaerobes

Facultative Anaerobes

  • Does not require oxygen for metabolism, but can grow in its presence

  • During minus oxygen states, anaerobic respiration or fermentation occurs

  • Possess superoxide dismutase and catalase

  • Ex. E. coli and S. aureus


Thioglycolate broth

Thioglycolate Broth

Thioglycollate broth is used to demonstrate aerotolerance of bacteria.

Aerobes, facultative anaerobes, and obligate anaerobes can be detected using this medium.


Other gas requirements

Other Gas Requirements

  • Microaerophiles - requires less than 10% of atmospheric O2.

    Ex: Campylobacter jejuni

  • Capnophiles - requires increased CO2 (5-15%) tension for initial growth.

    Ex: S. pneumoniae


Microbial nutrition and growth

pH

  • Most cells grow best between pH 6-8

  • Acidophiles (up to pH 0) - molds and yeast

  • Alkalinophiles (up pH 10) urea-decomposing bacteria like Proteus sp.


Osmotic pressure

Osmotic Pressure

  • Osmophiles - live in solutions with high solute concentration (e.g. sugar content in jams)

  • Halophiles - requires high salt concentrations and

    withstands hypertonic conditions

    Ex. Halobacterium sp. (Archaea)

  • Facultative halophiles - can survive high salt conditions but is not required for survival

    Ex. Staphylococcus aureus


Other factors

Other Factors

  • Radiation- withstand UV, infrared rays

  • Barophiles – withstand high pressures

  • Spores and cysts- can survive dry habitats


Microbial interactions

Microbial Interactions

Influence microorganisms have on other microbes:

  • Symbiotic relationship

  • Non-symbiotic relationship


Symbiotic relationship

Symbiotic Relationship

Organisms that live together in close nutritional relationships

Types:

  • Mutualism – both organism benefit

  • Commensalism – only one organisms benefits

  • Parasitism – typically host-microbe relationship


Commensalism

Commensalism

  • “Satellitism”

    as a form of commensalism

  • Staphylococcus aureus provides vitamins and amino acids to Haemophilus influenzae, which grows around colonies of S. aureus.


Non symbiotic relationships

Non-Symbiotic Relationships

  • Organisms are free-living, and do not rely on each other for survival

  • Types:

    • Synergism – shared metabolism enhances growth of both microbes

    • Antagonism- competition between microorganisms


Microbe host interactions

Microbe-Host Interactions

  • Can be commensal, parasitic, and synergistic

  • Ex. E. coli produce vitamin K for the host


Microbial growth

Microbial Growth

  • Binary fission

  • Generation time

  • Growth curve

  • Enumeration of bacteria


Binary fission

Binary Fission

  • Parent cell enlarges and duplicates its DNA

  • Septum formation divides the cell into two separate chambers

  • Complete division results in two identical daughter cells


Steps in binary fission

Steps in Binary Fission

Rod-shaped bacteria undergoing binary fission


Growth curve

Growth Curve

  • Lag phase

  • Log phase

  • Stationary phase

  • Death phase


Phases of bacterial growth

Phases of Bacterial Growth

Growth curve in a bacterial culture.


Enumeration of bacteria

Enumeration of Bacteria

  • Direct Methods:

    (a)Microscopic

    (b)Viable plate count

    (c)Membrane filtration

    (d)Most probable number

  • Indirect Methods:

    (a)Turbidity

    (b)Metabolic assay

    (c)Dry weight determinations


Direct microscopic count

Direct Microscopic Count

  • The direct cell method counts the total dead and live cells in a special microscopic slide containing a premeasured grid.

  • Petroff-Hausser counting chamber used in dairy industry.


Standard plate count

Standard Plate Count

Serially diluted samples are plated out and bacterial count expressed in CFU/ml.


Membrane filtration

Membrane Filtration

Membrane filtration and coliform counts.


Turbidimetric

Turbidimetric

Turbidimetric measurements as indicators of bacterial growth.

The greater the turbidity the larger the population density.


Coulter counter

Coulter Counter

  • The Coulter Counter uses an electronic sensor to detect and count the number of cells.

  • Rapid automated counting method


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